I've been banned from asking questions. But, when I checked all my past questions and answers, I've got a total of 6 downvotes. Is this enough to get a question ban? Or have I been banned due to inactivity in the past months?
Inactivity does not matter.
Question bans are automatically performed by the system. You can find out much more through a cursory search on meta. Or you can read this explanatory post.
In your case, I see that you have asked a total of 11 questions. Of these, 4 are closed and 3 have been deleted. Six are downvoted, 1 is at 0 score, and 4 are upvoted. On net, you have been downvoted 10 times more than you have been upvoted. This is not a good record.